One of the amazing things about the 8-bit Atari computers was how they could rewrite their display list on the fly, changing video modes every scan line. My favorite application of this was the rainbow effect. I’ve always wanted to know how to do this, and some searching led me to Alan Watson’s example in Compute!’s Second Book of Atari. I trimmed it down a bit to come up with this BASIC code, which you can run on a real Atari computer or in your favorite emulator: